/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.schemas;



import com.bff.gaia.unified.sdk.annotations.Experimental;

import com.bff.gaia.unified.sdk.annotations.Experimental.Kind;

import com.bff.gaia.unified.sdk.transforms.SerializableFunction;

import com.bff.gaia.unified.sdk.values.Row;

import com.bff.gaia.unified.sdk.values.TypeDescriptor;



import java.util.List;



/**

 * A {@link SchemaProvider} base class that vends schemas and rows based on {@link

 * FieldValueGetter}s.

 */

@Experimental(Kind.SCHEMAS)

public abstract class GetterBasedSchemaProvider implements SchemaProvider {

  /** Implementing class should override to return a getter factory. */

  abstract FieldValueGetterFactory fieldValueGetterFactory();



  /** Implementing class should override to return a type-information factory. */

  abstract FieldValueTypeInformationFactory fieldValueTypeInformationFactory();



  /** Implementing class should override to return a constructor factory. */

  abstract UserTypeCreatorFactory schemaTypeCreatorFactory();



  @Override

  public <T> SerializableFunction<T, Row> toRowFunction(TypeDescriptor<T> typeDescriptor) {

    // schemaFor is non deterministic - it might return fields in an arbitrary order. The reason

    // why is that Java reflection does not guarantee the order in which it returns fields and

    // methods, and these schemas are often based on reflective analysis of classes. Therefore it's

    // important to capture the schema once here, so all invocations of the toRowFunction see the

    // same version of the schema. If schemaFor were to be called inside the lambda below, different

    // workers would see different versions of the schema.

    Schema schema = schemaFor(typeDescriptor);



    // Since we know that this factory is always called from inside the lambda with the same schema,

    // return a caching factory that caches the first value seen for each class. This prevents

    // having to lookup the getter list each time createGetters is called.

    Factory<List<FieldValueGetter>> getterFactory = new CachingFactory<>(fieldValueGetterFactory());

    return o -> Row.withSchema(schema).withFieldValueGetters(getterFactory, o).build();

  }



  @Override

  @SuppressWarnings("unchecked")

  public <T> SerializableFunction<Row, T> fromRowFunction(TypeDescriptor<T> typeDescriptor) {

    Class<T> clazz = (Class<T>) typeDescriptor.getType();

    return new FromRowUsingCreator<>(

        clazz, schemaTypeCreatorFactory(), fieldValueTypeInformationFactory());

  }

}